1. Field of the Invention
The present invention generally relates to a rotary drive device. More specifically, the present invention relates to a rotary drive device provided with a vibrating body having a piezoelectric element and a rotating body that the vibrating body abuts against, wherein a voltage to the piezoelectric element causing the vibrating body to vibrate and thereby rotating the rotating body. The present invention further relates to a device equipped with such a rotary drive device.
2. Background Information
Rotary drive devices that use a piezoelectric element are already known. For example, Japanese Laid-Open Patent Publication No. 10-080164 discloses a rotary drive device that uses a piezoelectric element as described on pages 2 and 3 and illustrated in  FIG. 1 of this Japanese publication. The rotary drive device of this Japanese publication is provided with a base part, a vibrating body and a rotating body. The vibrating body is provided on the base part, and has a piezoelectric element. The rotating body is provided on the base part and abutted against by the vibrating body. The vibrating body is shaped like a circular disc and has an output shaft arranged along its rotational axis. The vibrating body abuts against the outer circumferential surface of the rotating body.
With this kind of rotary drive device, the rotating body can be rotated and drive power can be delivered via an output shaft by applying a voltage to the piezoelectric element, which in turn causes the vibrating body to vibrate. It is difficult to reduce the size of such a rotary drive device beyond a predetermined limit.
However, it has been discovered that since a vibrating body is provided on the outer circumference of the rotating body, the size of the rotary drive device is at least as large as the sum of the sizes of the rotating body and the vibrating body. Therefore, there is a limit to how small the device can be made when a prescribed drive torque is to be delivered.
The magnitude of the drive torque T of the rotary drive device is expressed as the product of the rotary force F and the distance r from the rotational center of the rotary shaft to the point where the rotary force F acts (here, the radius of the rotating body). Therefore, if the required torque is T1 and the rotary force F has a fixed magnitude, e.g., F1, then the radius R1 of the rotating body can be calculated and the size of the rotating body can be determined.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved rotary drive device. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.